Radio Frequency Heating Research Articles

Modeling of radio frequency heating of packed fluid foods moving on a conveyor belt: A case study for tomato puree

Computer simulation models were used to study radiofrequency heating of liquid foods moving on a conveyor belt between staggered-through field electrodes of non-uniform electric field distribution. Voltage across the electrodes was estimated using a finite-element model and a one-dimensional model, and these were utilized to simulate heating of tomato puree mixtures of varying dielectric and thermal properties, at various nominal voltages and electrode gaps. The experimental results for volume average temperatures showed good agreement with the outcome of both simulation models. Although the temperature profiles indicate a concentration of heat at the bottom and edges of the bottle, natural convection and the shape of the container helped mitigate heat localization. It was determined that, while simple models could provide accurate volume average temperatures, incorporating convectively enhanced conductivity was necessary to accurately predict temperature distribution. The heating rate was found to decrease with an increase in salt concentration. Industrial relevanceIn-package tunnel pasteurization is preferred over continuous-flow pasteurization for certain commercial products such as carbonated beverages or semi-solid foods of high viscosity. Dielectric heating can be applied in these cases with much lower requirements of floor space, water, and energy, while reducing heat losses and localized overheating. However, the radiofrequency heating of liquid foods has not been extensively studied, especially for in-package thermal treatments. A better understanding of the effect of various processing parameters on temperature distribution and heating rates could support a wider adoption of this technology in industrial processes.

Developing effective radio frequency and ultraviolet combination technology based on evaluating quality characteristics of buckwheat

Radio frequency (RF) heating and ultraviolet (UV) radiation are widely used in food processing. In this study, effects of RF and UV treatment alone and in combination on quality characteristics of buckwheat were investigated and compared under the operational parameters used for effective food decontamination. Results showed that RF heating at the high temperature (H-RF, 105 °C) led to significant changes on physicochemical properties of buckwheat, including an increase in water absorption capacity (WAC), and decreases in swelling power (SP), emulsifying capability (EC), foaming capacity (FC), viscosity capability, gelatinization enthalpy (ΔH), and rheological property. Correspondingly, intermolecular hydrogen bonds were broken, short-range order degree (ratio of 1047/1022 cm−1 and 995/1022 cm−1), crystallinity degree, and SH group contents were reduced. The changes of these parameters were mitigated by RF treatment at the low temperature (L-RF, 90 °C). While the UV radiation only affected the FC, EC, viscosity capability, and rheological property. Especially, UV radiation at low intensity (L-UV, 2.25 mW/cm2) alone did not significantly influence the multi-scale structures and physicochemical properties of buckwheat. Meanwhile, buckwheat treated by L-RF alone or in combination with L-UV performed the similar properties, implying that the UV treatment after RF heating could not further alter the quality of buckwheat. These results would provide basic information for the selection of suitable treatment to meet the needs of developing an effective treatment process.

Developing practical and small-scale radio frequency technology for tempering minced chicken breast at home

Radio frequency (RF) tempering, as a new tempering method suitable for overall heating applications, has been widely used for meat processing industry. However, an effective and uniform tempering process in a suitable RF system is still lacking for household applications. The cylindrical chicken breasts (Φ75 mm × 60 mm, Φ100 mm × 60 mm, and Φ125 mm × 60 mm) in a cubic polypropylene container were tempered in a newly self-built small-scale 50 Ω domestic RF heating system. Crushed ice was applied to surround the medium-size sample to improve the temperature distribution by matching the electric field behaviors in the RF tempering process. This study explored the effects of crushed ice assisted RF tempering (CIRFT) on heating behavior of test samples under three input power levels (300, 500, and 700 W) and three electrode gaps (80, 90, and 100 mm). The tempering performance between CIRFT and crushed ice assisted microwave tempering (CIMWT) were compared. The product quality [drip loss, color, pH value, and total volatile base nitrogen (TVBN) content] obtained through CIRFT, RFT, CIMWT, and MWT were compared. Results demonstrated that at the optimum CIRFT condition (500 W, 80 mm) the tempering rate and the heating uniformity of samples were improved as compared to RFT. In addition, the drip loss and TVBN content of the samples were relatively better with CIRFT than with RFT. Moreover, the better-quality attributes were obtained in RF treatments compared to MW tempering. Thus, CIRFT showed a positive effect on chicken tempering for household applications resulting in a rapid and uniform heating with a relatively greater retention of product quality.

Medical Imaging Compatibility of Magnesium- and Iron-Based Bioresorbable Flow Diverters.

Bioresorbable flow diverters are under development to mitigate complications associated with conventional flow-diverter technology. One proposed advantage is the ability to reduce metal-induced artifacts in follow-up medical imaging. In the current work, the medical imaging compatibility of magnesium- and iron-based bioresorbable flow diverters is assessed relative to an FDA-approved control in phantom models. Bioresorbable flow diverters, primarily composed of braided magnesium or antiferromagnetic iron alloy wires, were compared with an FDA-approved control flow diverter. The devices were assessed for MR imaging safety in terms of magnetically induced force and radiofrequency heating using 1.5T, 3T, and 7T field strength clinical scanners. The devices were deployed in phantom models, and metal-induced image artifacts were assessed in the 3 MR imaging scanners and a clinical CT scanner following clinical scan protocols; device visibility was assessed under fluoroscopy. The magnesium-based bioresorbable flow diverter, iron-based bioresorbable flow diverter, and the control device all demonstrated MR imaging safety in terms of magnetically induced force and radiofrequency heating at all 3 field strengths. The bioresorbable flow diverters did not elicit excessive MR imaging artifacts at any field strength relative to the control. Furthermore, the bioresorbable flow diverters appeared to reduce blooming artifacts in CT relative to the control. The iron-based bioresorbable flow diverter and control device were visible under standard fluoroscopy. We have demonstrated the baseline medical imaging compatibility of magnesium and antiferromagnetic iron alloy bioresorbable flow diverters. Future work will evaluate the medical imaging characteristics of the bioresorbable flow diverters in large-animal models.

Temperature uniformity of frozen pork with various combinations of fat and lean portions tempered in radio frequency

Radio frequency (RF) heating has potential commercial application for tempering frozen meat products with the main advantages of rapid and volumetric heating. However, edge-heating and runaway-heating are the main obstacles to large-scale industrial applications. RF tempering uniformity is closely related to the composition and distribution of the samples. In this study, twelve pork samples (8 × 8 × 8 cm3) composed of equal volumes of fat and lean but with different spatial distribution were taken as the research object to study the RF tempering uniformity with computer simulation method. Results showed that the tempering uniformity was closely related to the degree of compositions' aggregation and composition location in the sample. A lower degree of compositions’ aggregation enhanced the RF tempering uniformity, the improved maximum was 60%. Fat was heated faster than lean meat at the same treatment condition. Fat placed close to the upper electrode of the sample had a better tempering uniformity than placed close to the lower one, the TUI value decreased maximum was 0.071. With the same aggregation degree of equal amount components in the sample, thicker components had a positive impact on the RF tempering uniformity. The findings of this study provided a significant reference for meat industry to effectively apply RF tempering technology.

Numerical tools for burning plasmas

The software stack under development within a European coordinated effort on tools for burning plasma modelling is presented. The project is organised as a Task (TSVV Task 10) under the new E-TASC initiative (Litaudon et al 2022 Plasma Phys. Control. Fusion 64 034005). This is a continued effort within the EUROfusion inheriting from the earlier European coordination projects as well as research projects based at various European laboratories. The ongoing work of the TSVV Tasks is supported by the Advanced Computing Hubs. Major projects requiring the high performance computing (HPC) resources are global gyrokinetic codes and global hybrid particle-magnetohydrodynamics (MHD) codes. Also applications using the integrated modelling tools, such as the Energetic-Particle Workflow, based on the ITER Integrated Modelling & Analysis Suite (IMAS), or the code package for modelling radio-frequency heating and fast-ion generation may require intensive computation and a substantial memory footprint. The continual development of these codes both on the physics side and on the HPC side allows us to tackle frontier problems, such as the interaction of turbulence with MHD-type modes in the presence of fast particles. One of the important mandated outcomes of the E-TASC project is the IMAS-enabling of EUROfusion codes and release of the software stack to the EUROfusion community.

Nuclear fusion powered Titan aircraft

This paper discusses a system for Titan exploration enabled by nuclear fusion power. Titan is one of the most interesting locations in the solar system with a thick atmosphere, surface oceans, under-ice oceans and complex terrain. This paper provides a conceptual design of a fusion-powered system to explore many parts of Titan and enable the use of high-power instruments. The design includes a fusion-powered orbital transfer vehicle and an electric Titan science aircraft. A Direct Fusion Drive (DFD) propulsive engine could bring a sizable spacecraft to Titan orbit in less than two years. A second fusion reactor, configured as a closed-loop power generator, would be used for an electric Titan science aircraft. Both reactors are based on the Princeton Field-Reversed Configuration (PFRC) concept which combines an FRC with a magnetic mirror. PFRC uses a novel radio-frequency plasma heating system and deuterium-helium-3 fuel. A lower temperature plasma flows around the closed-field FRC region removing the fusion products. In the DFD propulsive configuration, this secondary flow permits direct and variable thrust and exhaust velocity. The science aircraft would do a powered entry to Titan and then have the capability to fly anywhere on the moon at subsonic speeds. The DFD-powered transfer vehicle would allow the in-orbit transfer stage to change inclination as needed to cover different areas of the surface.

Effect of thermal processing on debittering process and its impact on the functional properties of palmyrah young shoot flour

Palmyrah young shoot is rich in starch and fiber and provides good glycemic control. Unfortunately, the consumption rate is limited by the presence of bitter and toxic compounds. Reported literatures reveal that thermal treatment especially dry heat processes like milling the flour at more than 80 °C had an impact on toxicity reduction rather than wet heat processes like boiling. As a result, the current study was aimed to investigate the combined effect of wet (boiling) and dry (radio frequency) heat processing on the debittering of young shoot flour in comparison with tray drying. In the study the flour obtained by a combination of boiling and drying was considered as treated flour and without boiling and drying was considered as untreated flour. The combined effect of wet and dry heat processing had an impact on the nutrients but had no effect on bitterness reduction. The study found tray dried untreated flour favored the feasibility of bitterness reduction as compared to other samples. The compounds (FlabelliferinsB, Flabelliferins–II, isomers of flabelliferins, and vitamin C) responsible for bitterness and its intensity were identified by FTMS. Furthermore, the study revealed that debittering process improved the functional properties of young shoot flour compared to raw flour.

Advanced Radio Frequency Applicators for Thermal Magnetic Resonance Theranostics of Brain Tumors

Thermal Magnetic Resonance (ThermalMR) is a theranostic concept that combines diagnostic magnetic resonance imaging (MRI) with targeted thermal therapy in the hyperthermia (HT) range using a radiofrequency (RF) applicator in an integrated system. ThermalMR adds a therapeutic dimension to a diagnostic MRI device. Focused, targeted RF heating of deep-seated brain tumors, accurate non-invasive temperature monitoring and high-resolution MRI are specific requirements of ThermalMR that can be addressed with novel concepts in RF applicator design. This work examines hybrid RF applicator arrays combining loop and self-grounded bow-tie (SGBT) dipole antennas for ThermalMR of brain tumors, at magnetic field strengths of 7.0 T, 9.4 T and 10.5 T. These high-density RF arrays improve the feasible transmission channel count, and provide additional degrees of freedom for RF shimming not afforded by using dipole antennas only, for superior thermal therapy and MRI diagnostics. These improvements are especially relevant for ThermalMR theranostics of deep-seated brain tumors because of the small surface area of the head. ThermalMR RF applicators with the hybrid loop+SGBT dipole design outperformed applicators using dipole-only and loop-only designs, with superior MRI performance and targeted RF heating. Array variants with a horse-shoe configuration covering an arc (270°) around the head avoiding the eyes performed better than designs with 360° coverage, with a 1.3 °C higher temperature rise inside the tumor while sparing healthy tissue. Our EMF and temperature simulations performed on a virtual patient with a clinically realistic intracranial tumor provide a technical foundation for implementation of advanced RF applicators tailored for ThermalMR theranostics of brain tumors.

Disturbing Effect of Intra-Tissue Temperature Sensors in Pre-Clinical Experimental Studies of Radiofrequency Cardiac Ablation: A Computer-Based Modeling Study

Background: Preclinical studies on radiofrequency (RF) cardiac ablation (RFCA) use very small temperature sensors in specific positions in the tissue subjected to RF heating. Despite the sensors’ small size, the proximity to the ablation electrode and the extremely high thermal gradient around the electrode means that the presence of the temperature sensors could distort the temperatures recorded. Our objective was to assess the thermal impact of intra-tissue temperature sensors during RFCA. Methods: 3D RFCA models were built including different temperature sensors based on fiber optics and T-type thermocouples. Constant power ablation was simulated for 10 s. Results: The results showed that the disturbance caused by the presence of the T-type thermocouples was considerably greater (one order of magnitude) than that caused by the optical fibers. The closer the sensor was to the ablation electrode, the greater the greater the disturbance was and the more it increased with time in sensors more than 3 mm deep. The fiber optic measurements always slightly underestimated (<0.2 °C) the tissue temperature that would exist without the sensors, while the disturbance caused by the T-type thermocouples did not always result in underestimation but depended on the depth of the sensors parallel to the catheter. Conclusions: The presence of thermocouples inserted into the tissue close to the RF ablation electrode involves a disturbance that could affect the measured temperature value, although it does not substantially alter the shape and size of the thermal lesion. Optical fibers cause much less disturbance, possibly due to the absence of internal metal parts that favor heat conduction.

Combining Cryo-Thermal Therapy with Anti-IL-6 Treatment Promoted the Maturation of MDSCs to Induce Long-Term Survival in a Mouse Model of Breast Cancer.

Immunosuppression plays a significant role in tumor recurrence and metastasis, ultimately causing poor survival outcomes. Overcoming immunosuppression and stimulating durable antitumor immunity are essential for tumor treatment. In our previous study, a novel cryo-thermal therapy involving liquid nitrogen freezing and radiofrequency heating could reduce the proportion of Myeloid-derived suppressor cells (MDSCs), but the remaining MDSCs produced IL-6 by the NF-κB pathway, resulting in an impaired therapeutic effect. Therefore, here we combined cryo-thermal therapy with anti-IL-6 treatment to target the MDSC-dominant immunosuppressive environment, thereby optimizing the efficacy of cryo-thermal therapy. We found that combinational treatment significantly increased the long-term survival rate of breast cancer-bearing mice. Mechanistic investigation revealed that combination therapy was capable of reducing the proportion of MDSCs in the spleen and blood while promoting their maturation, which resulted in increased Th1-dominant CD4+ T-cell differentiation and enhancement of CD8+ T-mediated tumor killing. In addition, CD4+ Th1 cells promoted mature MDSCs to produce IL-7 through IFN-γ, indirectly contributing to the maintenance of Th1-dominant antitumor immunity in a positive feedback loop. Our work suggests an attractive immunotherapeutic strategy targeting the MDSC-dominant immunosuppressive environment, which would offer exciting opportunities for highly immunosuppressive and unresectable tumors in the clinic.

Fast ion generation by combined RF-NBI heating in W7-X

Good fast ion confinement in quasi-isodynamic stellarators still has to be demonstrated experimentally. In the absence of fusion alphas, auxiliary heating systems can be used to generate fast ions. For this purpose, W7-X has neutral beam injection and its newly installed ion cyclotron heating system. In practice, both systems can run simultaneously, the synergetic running of both is the focus of the current modelling development. With the upgrades to the SCENIC code described here, we find that, compared with pure neutral beam injection (NBI), the fast ion tail is significantly enhanced when radio frequency (RF) heating is enabled. But the effectiveness of heating and fast ion tail generation strongly depends on the plasma parameters and antenna frequency, which calls for further study, both numerical and experimental.

Developing a square container with ideal dielectric constant for improving radio frequency heating uniformity in low-moisture agricultural products

Developing a square container with ideal dielectric constant for improving radio frequency heating uniformity in low-moisture agricultural products

Honey De-crystallization by radio frequency heating for process efficiency: Computational monitoring combined with time domain nuclear magnetic resonance

Industrial de-crystallization of honey is carried out by using hot water or air at 60 °C or higher temperatures with the cost of energy and longer process times. The objectives of this study were to apply RF processing for de-crystallization and monitor this process with time-domain nuclear magnetic resonance (TD-NMR) data and a computational model. For this purpose, crystallized honey samples were processed in a 10 kW - 27.12 MHz free-running oscillator RF system, and experimental temperature data were used to validate the developed computational model. TD-NMR experiments were performed to monitor the de-crystallization, and the obtained kinetics data were coupled with temperature increase to compute the crystal content changes through the process. The RF de-crystallization led to a significant decrease (>70% compared to the conventional processes) in process time for industrial scale processing demonstrating its sustainability.

Pattern-Dependent Radio Frequency Heating of Laser-Induced Graphene Flexible Heaters.

Graphene is an excellent choice for heating applications due to its high thermal conductivity and is considered an interesting candidate for application in flexible heaters. The major challenge, though, is the costly and chemical-intensive pathways to produce graphene on a large scale. Laser ablation of polymeric substrates is a relatively recent technique for a facile, single-step, chemical-free fabrication of graphene, referred to as laser-induced graphene (LIG). This work demonstrates the fabrication of patterned LIG-based flexible heaters and their response to radio frequency (RF) electromagnetic waves. Polymeric substrates were scribed with laser patterns in both raster and vector modes and subjected to RF electromagnetic fields to test their heating response. We confirmed different graphene morphologies of the lased patterns through various materials characterization methods. The maximum steady-state temperature observed for the LIG heater was approximately 500 °C. Unprecedented heating rates, as high as 502 °C/s, were observed when LIG heaters were exposed to RF fields at 200 MHz frequency and 4.6 W power. Mechanical and thermal stability tests for the best heater were also performed showing a stable thermal response for 1000 bending cycles and 20 cycles of the heating test for 8.5 h, respectively. Our work suggests that LIG heaters produced in vector mode lasing outperformed those lased in raster mode which can be attributed to the improved graphene quality for RF absorbance.

A Numerical Analysis of Radio Frequency Heating of Coal With Different Ranks

AbstractRadio frequency (RF) heating is a novel thermal stimulation method in developing coalbed methane (CBM). Various research has been conducted on the effect of electromagnetic (EM) heating on the physical properties of coal. However, few studies considered the working conditions of underground coal seam heating. This paper calculates the coal seam temperature distribution based on the coupling between electromagnetic wave propagation and heat transfer in a vertical well to study the influence of coal seam metamorphism and thermoelectric characteristics on temperature distribution. The reservoir thermophysical parameters related to temperature are considered in the heat transfer and wave equations, respectively. Numerical simulations reveal the influence of coal ranks and thermo-electrical properties on heating efficacy. Results indicate that the temperature in the vicinity of the RF heater is relatively high, and the whole heated zone forms an elliptical shape. Low-metamorphism coal, such as lignite, is more functional for RF heating and has a broad heating range, leading to a uniform diffusion coefficient enhancement and good thermal homogeneity. Higher thermal conductivity, lower specific heat capacity, and water saturation can expand the heating area and reduce the temperature near the borehole, benefiting the maintenance of wellbore integrity. The coal seam relative permittivity has little effect on the reservoir temperature when its value is between 2.4 and 6.4.

Out-of-oven rapid synthesis of entropy stabilized oxides using radio frequency heating

Entropy stabilized oxides (ESOs) are a new class of stable hybrids and single phase metal oxides made from multiple ions with material properties somewhere between the constituent oxides, or occasionally entirely new properties. One of the limitations of ESOs is their energy-intensive fabrication process, which has resulted in slow development and scale-up of new ESOs. In this work, we present a novel energy-efficient ESO synthesis method that uses the ability of carbonaceous materials to heat rapidly in response to radio frequency (RF) fields in 1–200 MHz range. Using carbon fibers and graphene as RF susceptors, synthesis of (Mg0·2Co0·2Ni0·2Cu0·2Zn0.2)O is achieved through RF-initiated combustion synthesis with heating rates of 203 °C/s at 20 W of input power. This method reduces the formation time of ESOs to less than a minute, allowing for much more efficient fabrication. The corresponding morphology and composition of the as-synthesized ESO-carbon fiber and ESO-graphene were studied using extensive spectroscopy and characterization. Additionally, single carbon fibers coated with ESO were tested for tensile strength and modulus; little change in mechanical properties was observed as compared to pristine fibers. This work opens an exciting frontier for the rapid synthesis of ESO-carbon composites using RF heating as a non-contact, rapid, and efficient manufacturing process.

Closed-Loop Composite Welding and Bonding System Using Radio-Frequency Heating and Pressure

Polymer parts often replace traditional metallic parts in load-bearing applications due to their high strength-to-weight ratio, with thermoplastics at the forefront. Conventional manufacturing processes rely on using fasteners or adhesives to hold composite assemblies together, but thermoplastics can be welded together. Ultrasonic welding is widely used but becomes challenging for complex geometries, and new parameters need to be developed for different polymers and specimen geometries. In this work, we developed a closed-loop welding machine that employs the recent discovery of radio-frequency (RF) heating of carbonaceous materials. The machine is successfully able to weld polylactic acid (PLA) coupons with graphitic RF susceptors at the bondline in less than 2 min and using less than 50 W of input RF power. We found that a higher areal density of the graphitic paint lowers the mechanical properties of the weld because the carbonaceous materials hinder polymer chain diffusion. A significant change was not observed in weld properties for welding pressure ranges between 0 and 0.3 MPa. However, increasing out-of-plane welding displacement increased the modulus and strength of the weld. This work provides an interesting new automated system for welding polymer composites using RF fields, with potential applications in various manufacturing industries.

Modelling radio frequency heating of randomly stacked walnut kernels with different particle size

Modelling radio frequency heating of randomly stacked walnut kernels with different particle size

MRI of Implantation Sites Using Parallel Transmission of an Optimized Radiofrequency Excitation Vector.

Postoperative care of orthopedic implants is aided by imaging to assess the healing process and the implant status. MRI of implantation sites might be compromised by radiofrequency (RF) heating and RF transmission field (B1+) inhomogeneities induced by electrically conducting implants. This study examines the applicability of safe and B1+-distortion-free MRI of implantation sites using optimized parallel RF field transmission (pTx) based on a multi-objective genetic algorithm (GA). Electromagnetic field simulations were performed for eight eight-channel RF array configurations (f = 297.2 MHz), and the most efficient array was manufactured for phantom experiments at 7.0 T. Circular polarization (CP) and orthogonal projection (OP) algorithms were applied for benchmarking the GA-based shimming. B1+ mapping and MR thermometry and imaging were performed using phantoms mimicking muscle containing conductive implants. The local SAR10g of the entire phantom in GA was 12% and 43.8% less than the CP and OP, respectively. Experimental temperature mapping using the CP yielded ΔT = 2.5-3.0 K, whereas the GA induced no extra heating. GA-based shimming eliminated B1+ artefacts at implantation sites and enabled uniform gradient-echo MRI. To conclude, parallel RF transmission with GA-based excitation vectors provides a technical foundation en route to safe and B1+-distortion-free MRI of implantation sites.